1. Field of the Invention
The present invention relates to method and apparatus for heating and cooling a substrate such as the semiconductor wafer.
2. Description of the Related Art
In the photolithography process for manufacturing semiconductor devices, the surface of a semiconductor wafer is cleaned, dried by heat, and cooled. It is then coated by photoresist, pre-baked, cooled, pattern-exposed, developed and post-baked. It is further baked (or baking step just before the developing step) between the pattern-exposing step and the developing step and then cooled.
For example, the wafer is pre-baked to a temperature of about 80.degree. C. in a heating unit and it is post-baked to a temperature range of 50.degree. C.-180.degree. C. in other heating unit. After these baking steps, the wafer is cooled to room temperature (about 23.degree. C.) in a cooling unit. In the photolithography process, therefore, it is heated and cooled repeatedly and several times.
However, the conventional cooling unit is located remote from the heating unit. The wafer must be therefore carried from the heating unit into the cooling one. While it is being carried in this manner, its temperature changes variously, thereby making temperature distribution in its plane non-uniform. As the result, resist film becomes uneven in thickness and developing irregularities are thus caused.
A heat-treating apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-29203 is well-known as means for preventing the wafer from changing its temperature like this while it is being carried. This heat-treating apparatus includes a heater of the non-contact type arranged in a baking unit at the upper portion thereof, a cooling plate also arranged in it at its lower portion, and pins moved up and down while supporting the wafer horizontal in it.
In the conventional heat-treating apparatus, however, it is arranged that the wafer is heated by the heater attached to such a position that is above the wafer and not contacted with it. It takes therefore a long time and a lot of heat energy to heat the wafer to a high temperature of 180.degree. C., for example. In addition, it is difficult to make temperature distribution uniform in a plane of the wafer. Further, the heater and the cooling plate thermally interfere with each other because they are housed in the same unit.
Furthermore, the wafer is coated with chemically amplified resist, chemically-amplified resist changes its quality as time goes by after the wafer is post-baked. It must be therefore cooled for a short time after it is post-baked.